Knife sharpener



FIG. 1 is a perspective view of a knife sharpener.

FIG. 2 is a left side elevation view thereof.

FIG. 3 is a right side elevation view thereof.

FIG. 4 is a top view thereof.

FIG. 5 is a bottom elevation view thereof.

FIG. 6 is a front elevation view thereof; and,

FIG. 7 is a rear elevation view thereof.

The broken lines in FIG. 5 illustrate features of the knife sharpener that form no part of the claim. 

I claim the ornamental design for a knife sharpener, as shown and described. 